1. Field of the Invention
The present invention relates to a method of laser-welding metal sheets together, each of different thicknesses, resulting in a welded portion lacking a sharp edge.
2. Description of the Prior Art
To decrease weight and increase the rigidity of vehicles and to improve yield ratios of materials, one-piece materials are formed by laser-welding metal sheets having different thicknesses along abutting edges. The resulting assembly may be used as a press material for outer or inner body panels of vehicles.
Japanese Patent Publication SHO 63-168286 discloses laser-welding two metal sheets having different thicknesses together by linearly moving the laser beam along the weld line. In the laser welding, the laser beam axis is inclined from the vertical direction so that the laser beam is directed toward the thicker sheet. However, as illustrated in FIG. 16, with the conventional welding method, a sharp edge 2 remains at the corner of the thicker plate at the welded portion 1. To protect the press roll from galling while stamping such a laser-welded press material, the sharp edge must be removed by, for example, grinding after the sheets are welded. However, such grinding requires an additional manufacturing step and increases the cost to an unacceptably high level. Furthermore, in some cases, the strength of the panel is decreased as a result of over-grinding.